The rack and pinion type steering gear has been employed for the steering system of an automobile because of its lightness and its compactness. An automobile with front engine and front driving system is lighter because no long drive shaft is used, and accordingly, for the steering system, a light and small-sized rack and pinion type steering gear is employed. However, in this type steering gear, the rack is meshed with the pinion in a completely reversible manner, and therefore, a reaction force from a road surface is disadvantageously transmitted directly to the steering wheel. The overall steering ratio (the ratio of the wheels to the steering wheel) is usually 18 to 21 for a small automobile and 23 to 26 for a large automobile. If the steering ratio is so variable, that it is 18 to 21 at the neutral position of the steering wheel, or near its turning position from the netural position at slight angle in both directions and is 25 to 27 at the turning position of 200.degree. to 360.degree. of the steering wheel, then the rack and pinion type steering gear can be employed for an automobile having a displacement of 3,000 to 4,000 cc. If the steering gear has such a variable steering ratio, then light steering operation can be effected against the turning reaction force so as to keep the steering wheel proper, improve its stability and obtain a proper feeling of impact from the wheels.
In respect to the prior art rack and pinion type steering gear having a variable steering ratio, there is issued British Pat. No. 1,356,172 in which a rack has a pressure angle varied so as to vary the engaging pitch of the rack with the pinion; also, there are British Pat. Nos. 1,468,691 and 1,479,314 in which an intermediate gear is combined with a cam mechanism so as to vary the steering ratio of the steering gear. In the former patent, however, extremely difficult techniques and work are required to form a complicated tooth configuration corresponding to the varied pitch and pressure angle of the rack and the increasing overall steering ratio obtained by such a design is only 10 to 15 percent. In the latter patents, because more gears and the addition of a cam mechanism are required, the number of parts increases, which causes the construction to become complicated, and the volume of the gear increases.